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Register a new userClassical T Tauri-like Outflow Activity in the Brown Dwarf Mass Regime
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Over the last number of years spectroscopic studies have strongly supported the assertion that protostellar accretion and outflow activity persists to the lowest masses. In this paper we present the results of our latest investigation of brown dwarf (BD) outflow activity and report on the discovery of two new outflows. Here ISO-Oph 32 is shown to drive a blue-shifted outflow with a radial velocity of 10-20 km/s and spectro-astrometric analysis constrains the position angle of this outflow to 240 +/- 7 degrees. The BD candidate ISO-Cha1 217 is found to have a bipolar outflow bright in several key forbidden lines (radial velocity = -20 km/s, +40 km/s) and with a PA of 190-210 degrees. A striking feature of the ISO-Cha1 217 outflow is the strong asymmetry between the red and blue-shifted lobes. This asymmetry is revealed in the relative brightness of the two lobes (red-shifted lobe is brighter), the factor of two difference in radial velocity (the red-shifted lobe is faster) and the difference in the electron density (again higher in the red lobe). Such asymmetries are common in jets from low mass protostars and the observation of a marked asymmetry at such a low mass supports the idea that BD outflow activity is scaled down from low mass protostellar activity. In addition to presenting these new results, a comprehensive comparison is made between BD outflow activity and jets launched by CTTSs. In particular, the application of current methods for investigating the excitation conditions and mass loss rates in CTT jets to BD spectra is explored.
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A suite of discoveries in the last two decades demonstrate that we are now at a point where incorporating magnetic behavior is key for advancing our ability to characterize substellar and planetary systems. The next decade heralds the exciting maturation of the now-burgeoning field of brown dwarf magnetism, and investing now in brown dwarf magnetism will provide a key platform for exploring exoplanetary magnetism and habitability beyond the solar system. We anticipate significant discoveries including: the nature of substellar and planetary magnetic dynamos, the characterization of exo-aurora physics and brown dwarf magnetospheric environments, and the role of satellites in manifestations of substellar magnetic activity. These efforts will require significant new observational capabilities at radio and near infrared wavelengths, dedicated long-term monitoring programs, and committed support for the theoretical modeling efforts underpinning the physical processes of the magnetic phenomena
An investigation of the magnetospheric accretion and outflow signatures in sub-stellar objects is a natural extension of similar studies conducted on classical T Tauri stars (CTTS), and helps understand if brown dwarfs (BDs) follow the same formation mechanism as stars. Over the past decade, evidence for accretion in very low-mass stars (VLMs) and BDs has been accumulated using various techniques, which indicates that the overall accretion characteristics are continuous across the sub-stellar boundary. Outflow activity in VLMs and BDs has been confirmed based on spectro-astrometry of forbidden emission lines observed in the optical, and in millimetre continuum images of CO J=2-1 emission. This review summarizes the past and current state of observational work on accretion and outflow activity in VLMs and BDs, particularly with the advent of new instruments such as VLT/X-Shooter which has allowed the study of several accretion and outflow indicators over a wider wavelength range.
We present pre- and post-outburst observations of the new FU Orionis-like young stellar object PTF 10qpf (also known as LkHa 188-G4 and HBC 722). Prior to this outburst, LkHa 188-G4 was classified as a classical T Tauri star on the basis of its optical emission-line spectrum superposed on a K8-type photosphere, and its photometric variability. The mid-infrared spectral index of LkHa 188-G4 indicates a Class II-type object. LkHa 188-G4 exhibited a steady rise by ~1 mag over ~11 months starting in Aug. 2009, before a subsequent more abrupt rise of > 3 mag on a time scale of ~2 months. Observations taken during the eruption exhibit the defining characteristics of FU Orionis variables: (i) an increase in brightness by > 4 mag, (ii) a bright optical/near-infrared reflection nebula appeared, (iii) optical spectra are consistent with a G supergiant and dominated by absorption lines, the only exception being Halpha which is characterized by a P Cygni profile, (iv) near-infrared spectra resemble those of late K--M giants/supergiants with enhanced absorption seen in the molecular bands of CO and H_2O, and (v) outflow signatures in H and He are seen in the form of blueshifted absorption profiles. LkHa 188-G4 is the first member of the FU Orionis-like class with a well-sampled optical to mid-infrared spectral energy distribution in the pre-outburst phase. The association of the PTF 10qpf outburst with the previously identified classical T Tauri star LkHa 188-G4 (HBC 722) provides strong evidence that FU Orionis-like eruptions represent periods of enhanced disk accretion and outflow, likely triggered by instabilities in the disk. The early identification of PTF 10qpf as an FU Orionis-like variable will enable detailed photometric and spectroscopic observations during its post-outburst evolution for comparison with other known outbursting objects.
We report here the first results of a multi-wavelength campaign focussing on magnetospheric accretion processes within the close binary system V4046 Sgr, hosting two partly-convective classical T Tauri stars of masses ~0.9 Msun and age ~12 Myr. In this paper, we present time-resolved spectropolarimetric observations collected in 2009 September with ESPaDOnS at the Canada-France-Hawaii Telescope (CFHT) and covering a full span of 7d or ~2.5 orbital/rotational cycles of V4046 Sgr. Small circularly polarised Zeeman signatures are detected in the photospheric absorption lines but not in the accretion-powered emission lines of V4046 Sgr, thereby demonstrating that both system components host large-scale magnetic fields weaker and more complex than those of younger, fully-convective cTTSs of only a few Myr and similar masses. Applying our tomographic imaging tools to the collected data set, we reconstruct maps of the large-scale magnetic field, photospheric brightness and accretion-powered emission at the surfaces of both stars of V4046 Sgr. We find that these fields include significant toroidal components, and that their poloidal components are mostly non-axisymmetric with a dipolar component of 50-100G strongly tilted with respect to the rotation axis; given the similarity with fields of partly-convective main-sequence stars of similar masses and rotation periods, we conclude that these fields are most likely generated by dynamo processes. We also find that both stars in the system show cool spots close to the pole and extended regions of low-contrast, accretion-powered emission; it suggests that mass accretion is likely distributed rather than confined in well defined high-contrast accretion spots, in agreement with the derived magnetic field complexity.
Classical T Tauri stars (CTTSs) are young low-mass stellar objects accreting mass from their circumstellar disks. They are characterized by high levels of coronal activity as revealed by X-ray observations. This activity may affect the disk stability and the circumstellar environment. Here we investigate if an intense coronal activity due to flares occurring close to the accretion disk may perturb the inner disk stability, disrupt the inner part of the disk and, possibly, trigger accretion phenomena with rates comparable with those observed. We model a magnetized protostar surrounded by an accretion disk through 3D magnetohydrodinamic simulations. We explore cases characterized by a dipole plus an octupole stellar magnetic field configuration and different density of the disk or by different levels of flaring activity. As a result of the simulated intense flaring activity, we observe the formation of several loops that link the star to the disk; all these loops build up a hot extended corona with an X-ray luminosity comparable with typical values observed in CTTSs. The intense flaring activity close to the disk can strongly perturb the disk stability. The flares trigger overpressure waves which travel through the disk and modify its configuration. Accretion funnels may be triggered by the flaring activity, thus contributing to the mass accretion rate of the star. Accretion rates synthesized from the simulations are in a range between 10^-10 and 10^-9M_sun yr^-1 The accretion columns can be perturbed by the flares and they can interact with each other, possibly merging together in larger streams. As a result, the accretion pattern can be rather complex: the streams are highly inhomogeneous, with a complex density structure, and clumped
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